• Steven Rostedt's avatar
    ftrace: disable tracing for suspend to ram · f42ac38c
    Steven Rostedt authored
    I've been painstakingly debugging the issue with suspend to ram and
    ftraced. The 2.6.28 code does not have this issue, but since the mcount
    recording is not going to be in 27, this must be solved for the ftrace
    daemon version.
    
    The resume from suspend to ram would reboot because it was triple
    faulting. Debugging further, I found that calling the mcount function
    itself was not an issue, but it would fault when it incremented
    preempt_count. preempt_count is on the tasks info structure that is on the
    low memory address of the task's stack.  For some reason, it could not
    write to it. Resuming out of suspend to ram does quite a lot of funny
    tricks to get to work, so it is not surprising at all that simply doing a
    preempt_disable() would cause a fault.
    
    Thanks to Rafael for suggesting to add a "while (1);" to find the place in
    resuming that is causing the fault. I would place the loop somewhere in
    the code, compile and reboot and see if it would either reboot (hit the
    fault) or simply hang (hit the loop).  Doing this over and over again, I
    narrowed it down that it was happening in enable_nonboot_cpus.
    
    At this point, I found that it is easier to simply disable tracing around
    the suspend code, instead of searching for the particular function that
    can not handle doing a preempt_disable.
    
    This patch disables the tracer as it suspends and reenables it on resume.
    
    I tested this patch on my Laptop, and it can resume fine with the patch.
    Signed-off-by: default avatarSteven Rostedt <srostedt@redhat.com>
    Acked-by: default avatarRafael J. Wysocki <rjw@sisk.pl>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f42ac38c
main.c 16.1 KB